The shafts of land-based gas turbines and other land-based turbomachinery equipment are typically monitored by means of absolute vibration sensors that measure the absolute movement of the bearing external elements or by means of relative vibration sensors that measure the movement of the rotor of an assigned generator with respect to the bearing external elements. The values measured by the sensors, typically displacement, velocity, or acceleration vibration amplitude, are monitored with respect to maximum limit values. These limit values are defined taking into account the shaft mechanical integrity and clearances between rotor and casing elements. In some cases the measured signals are further analysed in the frequency domain and then compared to other appropriate limit values. In case the vibrations are too strong, the operation of the equipment is immediately interrupted by a protection system which sends the corresponding commands. The commands can comprise for example the closure of the fuel trip shut-valve in the case of a gas turbine, or the opening of a circuit breaker in electrical drive applications. Such state of the art monitoring and protection systems are very reliable for the detection of rotor bending vibrations, whereas they are not capable of performing a direct detection of rotor torsional vibrations.
The patent application US 2014109720 A1 however describes an engine subject to torsional vibrations comprising a torsional vibration damper generating a compensation torque by means of inertial masses via springs.
The U.S. Pat. No. 846,537 B2 describes a damping system for eliminating torsion vibrations of a shaft of a machine with a torque sensor and a magnetostrictive actuator device for generating a mechanical counter-vibration.